This application is based upon and claims the benefit of priority of Japanese Patent Application No. H. 11-258853 filed on Sep. 13, 1999, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electromagnetic valve for opening and closing a fluid passage, in particular, a shape of a seat member of the electromagnetic valve.
2. Description of the Prior Art
In a conventional electromagnetic valve, a fluid passage formed in a seat member is opened and closed in such a manner that, when magnetic attracting force generated by a solenoid portion drives a moving core, a valve body is driven together with the moving core to sit on a valve seat provided in the fluid passage or to leave from the valve seat. The seat member, which is formed generally in a ring or cylindrical shape, is fixed to a base member made of resin by inserting molding.
In the conventional electromagnetic valve, it is very difficult to position the seat member to correspond to a position of an opening of the base member when the seat member is fixed to the base member by inserting molding. Further, as the base member surrounds a circumference of the ring or cylindrical seat member, the seat member is likely to rotate in the base member after molding so that opening and closing control of the fluid passage may be adversely affected.
Furthermore, as shown in JP-A-10-38126, known is a cup shaped stopper for restricting a movement of the moving core on an opposite side of the vale body. The conventional stopper is made of non-magnetic material and fitted inside to a solenoid constituting member such as a yoke. However, such a construction has a drawback that a magnetic attracting force of the solenoid portion may be reduced because non-magnetic material stands in a gap between the moving core and the yoke.
To solve the problems mentioned above, it is thus an object of the present invention to provide an electromagnetic valve in which a valve seat is easily fixed to a base member by inserting molding and opening and closing of the fluid passage may be accurately controlled.
To achieve the above object, the seat member has means for positioning and preventing rotation. The means for positioning and preventing rotation serves to position the seat member and partly be surrounded by the base member when the base member surrounds the seat member by inserting molding so that the fluid passage may be accurately positioned to correspond to the opening of the base member, while the seat member is prevented from rotating in the base member after the inserting molding.
Preferably, the means for positioning and preventing rotation comprises a protruding portion having two parallel surfaces provided in the seat member or notches provided in the seat member. When the seat member is fixed to the base member by inserting molding, the two parallel surfaces or the notches of the protruding portion may be put between projecting portions of a pin of a molding die. As a result, the fluid passage of the seat member may be easily positioned to correspond to the opening of the base member. Further, after molding, the seat member may be prevented from rotating in the base member since the parallel surfaces or notches are partly covered by resin of the base member.
Further, it is another object of the present invention to provide an electromagnetic valve in which magnetic attracting force is stronger and an invasion of foreign material into the solenoid portion may be prevented.
To achieve the object, the electromagnetic valve has a stopper for restricting a movement of the moving member in a direction opposite to the valve at an end of the solenoid portion on an opposite side of the valve. This construction serves to generate a higher magnetic attracting force since there is no non-magnetic material in a gap between the moving core and the yoke.